Torque limiting clutches and couplers are well known in the art. Typically, they are placed between a drive source and a driven load to prevent damage to the drive system. A torque limiting clutch or coupler is interposed between a drive shaft and a driven shaft, interconnecting the drive source and driven load, to allow for slippage between the two at torque loads exceeding a predetermined level.
Typically, torque limiters such as the clutches and couplers just described comprise a plurality of interleaved friction and separator discs alternately splined to the drive and driven shaft, either directly or through appropriate hubs or housings. In such torque limiters, relative rotation of the shafts is accommodated by bearings at either end of the coupling device, such bearings typically being characterized by degrees of radial looseness. Such looseness, not only in the bearings, but also at the splines of the friction discs, gives rise to unacceptable levels of wear and corrosion on both the bearings and the splines, requiring the down time and cost incident to frequent repair and replacement of parts. Additionally, as wear and corrosion increases prior to the time for replacement or repair, the efficacy of the system is diminished.
Prior torque limiters have not attended to concentricities of the input and output hubs by providing for fixed interconnection between the output hub and a fixed friction end plate. Neither have such torque limiters provided for rigidity and alignment of the elements thereof by interconnecting a pair of end plates with a stack of separator plates therebetween, such interconnection being achieved by a plurality of torque pins. As a consequence of the shortcomings of the prior art structures, a pair of bearings, one at each end of the torque limiter, has been provided in some assemblies to assure reliable operation of the torque limiter.
The prior art of torque limiters further does not adequately provide for protection against axial thrusts in the shafts in both axial directions without significant risk of damage to the torque limiter system. In other words, while torque limiters are provided for torque protection, little thought is given to the impact of axial loads on the shafts with respect to the torque characteristics.
The prior art systems are totally unacceptable for use in massive, complex systems such as drive shafts of sea going vessels and the like. The time and cost involved in accessing and repairing torque limiters on such systems mandates that they not be given to defeat by wear and corrosion. Further, such systems are often exposed to significant changes in axial loads which, in the prior art, adversely impact the drive system and torque limiting capabilities.
For a number of reasons, including those presented above, the drive shafts of seagoing vessels have typically not employed friction-type torque limiters but, instead, have employed the rudimentary concepts of shear pins or the like. Such structures are not given to losses of effectiveness nor do they require service for corrosion and the like. However, when the shear pin performs its intended function, the sheared pin must be replaced. In systems such as the drive train of a seagoing vessel, such replacement time and costs are inordinate.